Circular CFDST short columns with hoops under compression: Comparative study and confinement models

Abstract

The circular concrete-filled double steel tubular (CFDST) column with hoops is a promising type of composite column, characterized by annular ribbed reinforcement bars welded onto the exterior surface of the steel tube. The confinement effect is expected to be enhanced by the inclusion of hoops, allowing for the use of thinner steel tubes and reducing overall steel consumption. In this paper, the compressive behavior of CFDST columns were experimentally and analytically investigated. The objectives are to gain insights into the different performance of CFDST columns from their counterparts without hoops and to evaluate different confinement models among double-tube, double-tube with hoops, and single-tube confined concrete. The test results indicated that hoops can improve the ultimate strength by 2 %–25 % for the CFDST columns, while the ductility of the CFDST columns can be significantly enhanced. Compared to increasing the cross-sectional area of steel tubes, incorporating hoops offers greater economic benefits for enhancing the strength of CFDST columns. The composite effect can be improved by the combined confinement provided by the double steel tubes and hoops. Comparisons of the test results with existing structural design provisions highlighted the necessity to account for the combined confinement effect of the double steel tubes and hoops on the structural response of CFDST columns. Accordingly, new confinement models were proposed to predict the ultimate strength of CFDST columns without and with hoops under axial compression.